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Biomedical subjects

R Martínez-García

Publications and source records attributed to R Martínez-García.

7 recordsLinked to original sources
PubMed2005

Effects of hormonal replacement with androgens and estrogens on male sexual behavior and plasma levels of these steroids in gonadectomized golden hamsters (Mesocricetus auratus).

Because the endocrine control of sexual behavior in male hamsters remains controversial, this study analyzed the influence of different androgens and estrogens in the regulation of masculine, sexual behavior (MBS). Aromatizable androgens: androstenedione (A) and testosterone (T), a non-aromatizable androgen: 5alpha-dihydrotestosterone (DHT), as well as estrogens (E2 and E1) alone or in combination with DHT, were administered in gonadectomized, sexually experienced males, for 3 weeks. In addition, plasma levels of these steroids were determined. Gonadectomy completely suppressed masculine sexual behavior (MSB) after 4 weeks. Both A and T replacements restored all the sexual behavior parameters in castrated hamsters by the 3rd week of treatment, with A being more potent in restoring all copulatory series and maintaining all MSB parameters, including long intromissions. Castrated males treated with DHT showed little interest in the female and did not display any copulatory behavior. Gonadectomized males treated with estrogens alone showed active anogenital investigation and displayed some mounts, but did not ejaculate. Males treated with estrogens combined with DHT had longer latencies and less number of ejaculations than males treated with aromatizable androgens. Long intromissions were observed only in males treated with T or A. Plasma levels of A were significantly higher than T levels in intact males. In males treated with A both androgens and estrogens were present in plasma. These results support the notion that aromatizable androgens, mainly A, but not non-aromatizable androgens or even estrogens in combination with DHT, play a relevant role in the endocrine regulation of MSB in the golden hamster.

Androgens↗
PubMed2004

Irreversible versus reversible aggregation: mean field theory and experiments.

Colloidal aggregation processes arising at different electrolyte concentrations were studied by means of experiments and confronted with theoretical predictions of different kinetic aggregation models. For this purpose, aqueous dispersions of relatively large polystyrene microspheres were chosen as experimental systems. Aggregation was induced by adding KBr electrolyte to the initially stable particle dispersions. During the aggregation processes, the cluster-size distribution was monitored by means of single cluster light scattering. Analyzing the time evolution of the monomer concentration, we found that the processes arising even at moderate electrolyte concentrations cannot be described by pure time-independent irreversible aggregation models. Hence, alternative models such as time-dependent irreversible aggregation and several reversible aggregation models were also tested. The model that considers a time-dependent sticking probability was found to fit the data quite satisfactorily. Nevertheless, the fitted was so slow that it seems not very likely to find such a behavior in real systems. The aggregation-fragmentation models reported in the literature were unable to reproduce the experimental observations. Hence, a more realistic reversible aggregation model was developed. This model accounts also for reenforced or double bonds between the constituent particles. The corresponding fit improved significantly and reached the same quality as the time-dependent model. Moreover, the obtained fitting parameters were in qualitative agreement with the DLVO predictions and so, reversible aggregation seems to be a more reasonable explanation for the experimental data than time-dependent irreversible aggregation. However, no definite statement on the possible secondary bond fragmentation mechanism may be made since both the applied shear stress in the measuring cell and thermal fluctuations can cause weaker bonds to break.

Journal Article↗
PubMed2003

Changes in masculine sexual behavior, corticosterone and testosterone in response to acute and chronic stress in male rats.

Chronic exposure to stressors increases HPA axis activity and concomitantly reduces HPG axis activity. This antagonistic relationship between both these axes has been proposed to underlie the inhibition of reproductive function due to stress. Sexual behavior in males may be the most vulnerable aspect of male reproduction to acute and chronic stress and it has been suggested that alterations in sexual behavior during stress are due to the antagonistic relationship between testosterone and corticosteroids. However, only in a few studies has a correlation between the levels of testosterone and corticosterone, and sexual behavior been made. In this study, we evaluated the effects of different stressors, applied both acute and chronically, on masculine sexual behavior and whether or not these effects on sexual behavior are accompanied by changes in plasma levels of corticosterone and testosterone. Additionally, we evaluated the effect of testosterone treatment on the effects of stress on sexual behavior. Sexually experienced male rats were exposed to one of the following stressors: immobilization (IMB), electric foot shocks (EFS) or immersion in cold water (ICW). Sexual behavior and plasma levels of testosterone and corticosterone were assessed on days 1, 5, 10, 15, and 20 of stress. In a second experiment, males were castrated, treated with 3 different doses of testosterone propionate (TP) and exposed to ICW for 20 consecutive days. Sexual behavior was assessed on days 1, 5, 10, 15, and 20 and steroids were evaluated on day 20. Parameters of masculine sexual behavior were modified depending on the characteristics of each stressor. Mount, intromission and ejaculation latencies increased significantly, the number of mounts increased, and ejaculations decreased significantly in males exposed to EFS and to ICW but not in males exposed to IMB. Associated with these effects, testosterone decreased in the EFS and ICW groups on days 1, 15, and 20. However, corticosterone increased only in males exposed to ICW. In castrated males, TP treatment failed to block the effects of stress by ICW on sexual behavior and corticosterone. These results indicate that the effects of stress on sexual behavior depend on the characteristics of each stressor, and these effects, as well as the decrease in testosterone are not necessarily associated with the increase in corticosterone. The fact that testosterone treatment did not prevent the effects of stress on sexual behavior suggests that other mediators could be involved in the alterations of sexual behavior caused by stress.

Acute Disease↗
PubMed2003

Body weight gain and diurnal differences of corticosterone changes in response to acute and chronic stress in rats.

Plasmatic levels of corticosterone display a circadian rhythm, with the higher values occurring during the dark phase in nocturnally feeding animals. Stressful situations induce a rise of corticosterone levels and this endocrine response to stress also presents circadian variations. The higher increase of corticosterone in response to stress occurs when the hormone is in its lower circadian level, and the minimum responses occurring at the peak. Since it has been shown that plasma hormones respond differently to different stressors, in the present study, we compared the acute and chronic effects of four different stressors: electric foot shocks (3 mA, 1/s, 5 min), immobilization during two hours or six hours, and immersion in cold water (15 degrees C) for 15 min. Stressors were applied, both acutely and chronically (during 4, 12 and 20 days) at the onset of the light phase as well as at the onset of the dark phase of the light/dark cycle. Body weight was assessed every day, and at the end of the manipulations plasmatic corticosterone levels were determined from the trunk blood. Adrenal and testicular weights were also assessed. Acute exposure to stressors increased plasmatic corticosterone levels significantly when the stressors were applied at the beginning of the light phase of the cycle. In the dark phase, only two hours of immobilization and immersion in cold water caused an increase in plasmatic corticosterone. With repeated exposure, electric foot shocks failed to induce significant changes in corticosterone levels in any phase of the light-dark cycle. Immobilization stress induced a significant rise in corticosterone levels only when the stressor was applied during the light phase. Immersion in cold water elicited a clear increase in plasmatic corticosterone levels in all the periods tested, regardless of the time of the cycle in which the stressor was applied. We did not observe a loss in body weight, but rather a smaller weight gain in stressed rats. Body weight gain was minimum in rats exposed to immersion and 6 hours of immobilization. Adrenal hypertrophy was observed in rats exposed to these same stressors. We conclude that: 1) the activation of the hypothalamus-pituitary-adrenal axis by stress depends mainly on the characteristics of the stressor; 2) the response of this axis to stress also depends on the time of day in which the stressor is applied.

Acute Disease↗
PubMed2002

Constant bond breakup probability model for reversible aggregation processes.

Reversible aggregation processes were simulated for systems of freely diffusing sticky particles. Reversibility was introduced by allowing that all bonds in the system may break with a given probability per time interval. In order to describe the kinetics of such aggregation-fragmentation processes, a fragmentation kernel was developed and then used together with the Brownian aggregation kernel for solving the corresponding kinetic master equation. The deduced fragmentation kernel considers a single characteristic lifetime for all bonds and accounts for the cluster morphology by averaging over all possible configurations for clusters of a given size. It became evident that the simulated cluster-size distributions could be described only when an additional fragmentation effectiveness was considered. Doing so, the stochastic solutions were in good agreement with the simulated data.

Journal Article↗
PubMed2001

Prognostic factors for response to sildenafil in patients with erectile dysfunction.

OBJECTIVE: To assess the clinical efficacy of sildenafil as treatment for erectile dysfunction (ED) the factors associated with treatment failure were investigated. METHODS: Open, prospective study including 244 patients suffering from ED who were evaluated by anamnesis, physical exploration, blood test, dynamic penile color duplex ultrasonography and Sexual Health Inventory for Male (SHIM). The efficacy of sildenafil was assessed by repeating the SHIM 2 months after therapy, independent of the final dose used. Side effects were also recorded. Factors influencing treatment outcome were evaluated by univariate and multivariate statistical analysis. RESULTS: Overall, sildenafil was effective in 56.8% of 213 eligible patients. When the etiologic diagnosis was not included in the multivariate analysis, antecedents of diabetes mellitus, non-nerve-sparing radical prostatectomy and SHIM basal score were selected as predictors of a poor response. In a second analysis including etiologic diagnosis, only SHIM basal score and etiological diagnosis proved to be of prognostic value. Side effects were noticed by 24.4% of patients, none of them being severe. CONCLUSIONS: Sildenafil is a rather effective and well-tolerated treatment for ED. The basal severity of ED and etiological diagnosis are the prognostic factors most significantly associated with treatment outcome.

3',5'-Cyclic-GMP Phosphodiesterases↗